Devices and methods for adaptive crest factor reduction in dynamic predistortion

ABSTRACT

A non-linear pre-distortion engine maintaining constant peak power at its output is disclosed. The engine includes a compression estimator, a crest factor reduction processor, a digital pre-distorter and a power amplifier. The compression estimator is configured to generate a compression estimate based on an input signal and a feedback signal. The feedback signal is based on an RF output signal. The crest factor reduction processor is configured to reduce a crest factor of the input signal to generate a crest factor reduced signal based on the compression estimate. The digital pre-distorter is configured to apply a pre-distortion to the crest factor reduced signal after an initial phase and generate a pre-distorted signal based on pre-distortion parameters. The power amplifier is configured to amplify the pre-distorted signal to generate the RF output signal. The operation of the chain consisting of pre-distorter and power amplifier is substantially linear and the pre-distorter maintains constant peak power at its output, which eliminates unwanted avalanche or pre-distorter blow-up issues.

BACKGROUND

Communication systems often use transmission signals focused around acarrier frequency of a defined channel. Information is conveyed byrepresenting the information with a modulation based on amplitude,phase, frequency and/or combinations thereof. The information is sent byone or more signals over a band of frequencies around the carrierfrequency.

A radio frequency (RF) power amplifier is often used for modulations,such as amplitude modulation. The RF power amplifier is required tooperate over wide ranges of frequencies and power levels. Ideally,perfect linearity over the ranges of frequencies and power levels isdesired. However, perfect linearity is impractical to realize in realsystems. As a result, RF power amplifiers typically introduce unwanteddistortions due to their non linearity. These distortions degradecommunications and impact performance.

However, the RF power amplifier typically includes non linearity andintroduces unwanted distortions into its output signal. Thesedistortions degrade communications, degrade efficiency and negativelyimpact performance. Additionally, intermodulation of input signalcomponents can occur and cause undesirable interference. Theintermodulation products can also extend outside the allowed bandwidthand cause undesirable interference and violate transmitting licensingand regulatory spectral emission requirements.

One technique to reduce the RF power amplifier introduced distortions isto apply a predistortion the to the amplifier input signal. Thepredistortion attempts to compensate for the amplifier-introduceddistortions and improve the linearity of the cascade consisting ofpre-distorter and RF power amplifier. The typical algorithms used forpredistortion are intended to tune their parameters and minimize thetotal error between the desired reference signal and an observed signal.However, the amount or degree of linearization actually achieved canvary substantially according to both instantaneous characteristics ofthe reference signal being pre-distorted and the amplifier's transfercharacteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a non-linear pre-distortionengine that mitigates in band and out of band distortions.

FIG. 2 is a block diagram illustrating a peak estimator.

FIG. 3 is a block diagram illustrating a peak normalizer.

FIG. 4 is a diagram illustrating a compression estimator.

FIG. 5 is a graph illustrating example power curves for a poweramplifier using a pre-distortion approach based on constant averagepower scaling.

FIG. 6 is a graph illustrating example power curves for a poweramplifier using a pre-distortion approach based on constant peak power.

FIG. 7 is a flow diagram illustrating a method of operating a non-linearpre-distortion engine having constant peak power.

DETAILED DESCRIPTION

The present invention will now be described with reference to theattached drawing figures, wherein like reference numerals are used torefer to like elements throughout, and wherein the illustratedstructures and devices are not necessarily drawn to scale.

Systems, methods, devices and embodiments are provided that implementpre-distortion for an RF power amplifier that uses adaptive tuning of acrest factor reduction processor in combination with a digitalpre-distorter. These can be used in a variety of applications thatinclude non-linear pre-distortion engines (NLPEs) for applicationsincluding, but not limited to, power amplifiers in wireless basestations, line drivers in wireline transceivers, electrical to opticalconverters for optical fiber communication transceivers, power amplifiertest and characterization equipment, and the like.

A list of abbreviations used hereinafter:

ACPR Adjacent Channel Power Ratio

AM-AM Amplitude Modulation—Amplitude Modulation

CE Compression Estimator

CFRP Crest-Factor Reduction Processor

DPD Digital Pre-Distorter

EVM Error Vector Magnitude

NLPE Non-Linear Pre-distortion Engine

PE Peak Estimator

PN Peak Normalizer

SEM Spectral Emission Mask

TA Time Alignment

RF power amplifiers typically exhibit non-linearity over at leastportions of their range of operating frequencies and/or power levels.The non-linearity of a power amplifier introduces unwanted distortionsinto its output signal. The unwanted distortions include out-of-banddistortions and in-band distortions. These unwanted distortions,especially in-band distortions, degrade communications, degradeefficiency and negatively impact performance. The out of banddistortions typically result from intermodulation of input signalcomponents. The intermodulation products can also extend outside theallowed bandwidth and cause undesirable interference and violatetransmitting licensing and regulatory spectral emission requirements.

The examples described herein can be used to address a number ofchallenges that other linearity pre-distortion systems do not.Sufficient out of band suppression, typically quantified in terms ofadjacent channel power ratio (ACPR) and spectral emission mask (SEM), isachieved. In band distortion is maintained below a specified level,which is typically characterized in terms of an error vector magnitude(EVM) constraint. Selected output power is maintained while avoidingexcessive signal peaks at the non-linear pre-distortion engine (NLPE)output and the RF power amplifier input.

FIG. 1 is a block diagram illustrating a non-linear pre-distortionengine (NLPE) 100 that mitigates in-band and out-of-band distortions.The engine 100 is a closed loop complex baseband engine and uses anindirect learning architecture. It is appreciated that the NLPE 100 isprovided in a simplified format and that other components can beemployed.

Generally, the engine 100 includes a compression ratio estimate portion136 and a peak power portion 138. The compression ratio estimate portion136 generates an estimate of the compression ratio caused by alinearization process. The peak power portion 138 is configured tomaintain a constant peak power for an input to a power amplifier.

In particular, the NLPE 100 includes a crest factor reduction processor(CFRP) 102, a compression estimator 104, a peak estimator 106, a firstdigital pre-distorter (DPD) 108, a learning algorithm component 110, asecond or post digital pre-distorter (DPD) 112, a second peak estimator114, a peak normalizer 116, a time alignment (TA) component 118, anon-linear power amplifier 120, an up-conversion component 140 and adown-conversion component 142.

The engine 100 receives an input signal x and generates an RF signal asits output. The input signal x typically includes modulation components,such as phase modulation, amplitude modulation and the like that conveyinformation. The RF signal can be used for transmission to anotherdevice or component external to the engine 100.

The CFRP 102 is configured to reduce a crest factor of the input signalx and provide the reduced signal at its output. The output of the CFRP102 is referred to as a crest factor reduced signal and is provided toan input of the first DPD 108. The CFRP 102 is configured to fulfillrequirements, such as error vector magnitude (EVM) and adjacent channelpower ratio (ACPR) requirements. Typically, the EVM is reduced to orbelow a threshold value as required. The EVM can be specified inregulatory requirements. Similarly, the ACPR is also reduced to or belowa threshold value.

The first DPD 108 receives the crest factor reduced signal from the CFRP102 and is configured to apply a pre-distortion and provide apre-distorted signal at its output. The pre-distorted signal is providedas an input to the power amplifier 120. Generally, the DPD 108 appliespre-distortions to compensate for non-linearity distortion introduced bythe power amplifier 120. It is noted that the up-conversion component140 up converts the pre-distored signal to an RF band prior to beingprovided to the input of the power amplifier 120.

The CFRP 102 ensures that the crest factor of an input of the DPD 108 isset to or below an initial value—the peak to average power ratio (PAPR),referred to as PAPR_(in), during an initial phase where t<T and Trepresents a duration of the initial phase. Additionally, the DPD 108leaves its input signal unaltered during the initial phase. Thus, theDPD 108 passes the crest factor reduced signal as the pre-distortedsignal.

The output of the power amplifier 120, the RF signal, is recorded, timealigned with the input signal x, and scaled by mixer 130 to obtain afeedback signal y, also referred to as a feedback or result signal. Thecompression estimator 104 uses the feedback signal y and the inputsignal x to generate or yield an estimate of an average power differencebetween the input signal x and the feedback signal y. This estimatedpower difference Δ{circumflex over (P)} (also referred to as compressionestimate) is equal to the power drop caused by the real power amplifierdue to compression compared to a perfectly linear power amplifier. Thecompression estimate is shown as Δ{circumflex over (P)} of thecompression ratio

${\Delta \; P} = {{{\frac{{\overset{\_}{P}}_{out}}{{\overset{\_}{P}}_{out}^{\prime}}.\Delta}\; \hat{P}} = {\frac{{x}_{2}}{{y}_{2}} = \frac{\sum\limits_{k}^{\;}{x_{k}}^{2}}{\sum\limits_{k}^{\;}{y_{k}}^{2}}}}$

where x is the input signal, y is the feedback signal and k is thenumber of samples.

As described above, the input peak-to-average-power ratio during theinitial phase is

${PAPR}_{i\; n} = {\frac{{\hat{P}}_{i\; n}}{{\overset{\_}{P}}_{i\; n}}.}$

Automatic peak scaling makes sure that the peak power beforelinearization (denoted {circumflex over (P)}_(in)) is equal to the peakpower after linearization (denoted {circumflex over (P)}_(in)′).

The compression estimate Δ{circumflex over (P)} 122 is provided to theCFRP 102. After the initial phase (t≧T), the CFRP 102 is configured toreduce the envelope-peak

${x}_{\infty} = {\max\limits_{k}{x_{k}}}$

of its input x by Δ{circumflex over (P)} yielding a crest factor

${PAPR}_{i\; n}^{\prime} = {\frac{{PAPR}_{i\; n}}{\Delta \; P}.}$

Additionally, the CFRP 102 spectrally shapes the resulting distortionsuch that requirements, such as EVM and ACPR requirements, are compliedwith. In one example, the CFRP 102 is configured to estimate thespectral shape of the input x in order to ensure proper spectral shapingof the distortion.

The peak estimator 106 facilitates generation of the feedback signal (y)128 used by the compression estimator 104. The peak estimator 106operates on a block or stream of complex valued baseband samples. Anenvelope magnitude is determined for the block of samples. Thereal-valued and positive envelope block is interpolated by a factor K inorder to capture peak re-growth effects. Then, the maximum value of theoversampled block is tracked yielding a peak estimate {circumflex over(x)}. Additional details on the operation of and configuration of asuitable peak estimator are shown below.

The time alignment component 118 is configured to receive a coupledversion of the RF output signal and time align the output signal withthe input signal x. The coupled version of the RF output signal has beendown converted from an RF frequency to baseband by the down-conversioncomponent 142. The peak normalizer 116 is configured to receive the timealigned RF output signal and to normalize the signal with respect to itspeaks. The peak normalizer 116 provides its output as a peak normalizedsignal, which is provided to the multiplier 132 and the multiplier 130.

The peak normalized signal can be shown as:

$\overset{\sim}{x} = {\frac{x}{{x}_{\infty}} = \frac{x}{\max\limits_{k}{x_{k}}}}$

where x is the input signal and the peak normalizer 116 uses k samples.

The peak normalized signal is provided to the multiplier 130, whereinthe output of the peak estimator 106 is combined with the peaknormalized signal to generate the feedback y. Additionally, the peaknormalized signal is provided to the multiplier 132, where it iscombined with a second peak estimator signal from the second peakestimator and provided to the second DPD 112.

The first DPD 108 generates the pre-distorted signal and the second DPD112 generates a pre-distorted feedback signal based at least partly onthe peak normalized output signal. A subtraction component 134 isconfigured to combine the pre-distorted signal and the pre-distortedfeedback signal and provide the combined signal to the learningalgorithm component 110.

The learning algorithm component 110 is configured to generatepre-distortion parameters 126 based on the combined signal from thesubtraction component 134. The pre-distortion parameters 126 areprovided to both the first DPD 108 and the second DPD 112 so bothprovide the same pre-distortion to their input signals. As a result, thepre-distorted signal is used as the input to the power amplifier 120 andhas a substantially constant peak power.

FIG. 2 is a block diagram illustrating a peak estimator 200. The peakestimator 200 can be used, for example, in the system 100 as components106 and/or 114. The peak estimator 200 is provided for illustrativepurposes and it is appreciated that variations and/or implementationsare permitted.

The peak estimator 200 includes an absolute value component 202, aninterpolator 204 and a max function component 206. The absolute valuecomponent 202 receives a signal 208, such as the input signal x, andperforms an absolute value on the signal and generates its absolutevalue as an output signal 210. Thus, the output signal 210 is always apositive value.

The interpolator 204 samples and oversamples the signal 210 based on Ksamples. The signal 210 typically is considered to have blocks specifiedby a duration and/or number of symbols and the oversampling is performedon a block of the signal 210. Thus, for an example block, if K=4, thereare 4 samples and 9 interpolated samples for a total of 13 oversamples.The oversamples are provided as an output 212 of the interpolator.

The max function component 206 reviews the oversamples 212 for the blockand identifies a maximum or peak value. This peak value is provided as apeak estimate 214. A revised or new estimate is determined for eachadditional block.

FIG. 3 is a block diagram illustrating a peak normalizer 300. The peaknormalizer 300 is an example of a suitable peak normalizer that can beused in the system 100 as component 116, described above. It isappreciated that other implementations and variations for the peaknormalizer are contemplated.

The peak normalizer 300 receives an input signal 306, such as x, andgenerates a normalized signal 308 at its output. The normalized signal308 typically falls within a range of values with an upper bound atabout 1due to the normalization. The normalization is for one or moreblocks, in one example.

The peak normalizer 300 includes an input terminal 310, a divider 304and a peak estimator 302. The input terminal 310 is configured toreceive the input signal 306. In one example, the input signal 306 is acoupled version of an RF output signal that has been time aligned withanother signal. The peak estimator 302 is configured to receive theinput signal 306 and generate a peak estimate over one or more blocks ofdata of the input signal 306. The peak estimate is provided as a peakoutput signal to the divider 304.

The divider 304 divides the input signal 306 by the peak estimate fromthe estimator 302. As a result, the divider 304 generates and providesthe normalized signal 308 at its output. The divider 304, in oneexample, operates on samples of the input signal and produces normalizedvalues for each sample, divided by the peak estimate. The dividertypically uses the same peak estimate per block of the input signal 306.

In one variation, a multiplier is used instead of the divider 304 andthe peak estimate is inverted prior to multiplying.

FIG. 4 is a diagram illustrating a compression estimator 400. Thecompression estimator is provided as an example of a suitablecompression estimator that can be used in the system 100, describedabove. It is appreciated that other implementations and variationsthereof are contemplated.

The compression estimator 400 provides a comparison of a first signal414 and a second signal 416. The comparison is provided in the form of aratio and is provided as a compression estimate 418. The compressionestimate 418 is based on one or more blocks of the signals 414 and 416.

Compression with regards to a power amplifier, such as amplifier 120shown above, refers to a region where the amplifier output signal nolonger increases linearily with the amplifier input signal. Beyond acompression threshold, the incremental gain in the amplifier outputsignal starts decreasing for given amplifier input values. The amplifieroutput signal compresses towards the input signal.

The compression estimator 400 generates the compression estimate 418,which allows a CFRP component to reduce the crest factor of a signal bythe compression estimate 418 and mitigate unwanted compression.

The compression estimator 400 generates an average power for the firstsignal 414 and an average power for the second signal 416 and thendivides the first average power by the second average power to generatethe compression estimate 418. In one example, the first signal 414 isthe input x and the second signal 416 is the feedback signal y describedabove with regard to FIG. 1.

A first side of the compression estimator 400 includes a first magnitudecomponent 402, a first summation component 420, and a first integrator404. The first side determines an average power for the first signal414. The magnitude component 402 squares its input, which always resultsin a positive value. Its output is added to an output of the firstintegrator 404 at the summation component 420. An output of thesummation component 420 is integrated by the first integrator 404. Theoutput of the first integrator is provided to a multiplier/combiner 406and represents an average power of the first signal 414 and is alsoprovided to the first summation component 420 as feedback.

A second side of the compression estimator 400 includes a secondmagnitude component 412, a second summation component 422, a secondintegrator 410, and an inverse component 408. The second side determinesan average power for the second signal 416. The second magnitudecomponent 412 squares its input, which results in a positive value. Itsoutput is added to an output of the second integrator 410 at the secondsummation component 422. An output of the summation component 422 isintegrated by the second integrator 410. The output of the secondintegrator 410 is inverted by component 408 and then provided to amultiplier/combiner 406 and represents an average power of the secondsignal 416. The output of the second integrator 410 is also provided tothe second summation component 422 as feedback.

FIG. 5 is a graph 500 illustrating example characteristics of a poweramplifier using a pre-distortion approach based on constant averagepower scaling. The curves are examples of a pre-distortion engine thatmaintains constant average power before linearization (that is, beforeand during the initial phase, t<T) and after linearization (t>=T). Theamplifier characteristic is described in form of amplitude modulation toamplitude modulation (AM-AM) curves.

The graph 500 includes an x-axis that represents increasing input powerto a power amplifier and a y-axis that represents increasing outputpower from the power amplifier. The power amplifier is a type used, forexample, in RF communications and the like. The curves or lines depictoutput power values for given input power values.

Line 502 represents the AM-AM behavior of the power amplifier (withoutlinearization). It can be seen that the behavior is non-linear. This isan example of typical power amplifier behavior without correction. Line504 represents behavior from a non-linear pre-distorter. Thepredistortion 504 attempts to compensate for distortions introduced bythe power amplifier.

The combination of the predistortion and the AM-AM behavior isrepresented by line 506. The combination 506 is the result of the poweramplifier characteristics and the non-linear pre-distortion engine. Itcan be seen that the combination 506 is substantially linear. Thecombination yields the same average power amplifier output power P_(out). The pre-distortion 504 counters compression exhibited by thepower amplifier 502 by exhibiting expansive behavior.

This approach depends on a learning algorithm that determines thecoefficients or parameters for the pre-distortion. Estimation errors,such as measurement noise, numerical noise, suboptimal model choice,imperfect equipment configuration, parameter drift and the like cancreates severe expansion characteristics at upper power amounts. Theseunwanted effects are referred to as pre-distorter blow up, avalancheeffect and the like and can have deleterious consequences for the poweramplifier and system/device it is in. Additionally, there is no controlover peak power of the pre-distortion 504 and/or of the power amplifierusing this approach.

FIG. 6 is a graph 600 illustrating example power curves for a poweramplifier using a pre-distortion approach based on constant peak power.The curves are examples associated with a pre-distortion engine thatmaintains a constant peak power. The curves are examples of curves thatcan be obtained using the system 100 and variations thereof.

The graph 600 includes an x-axis that represents increasing input powerto a power amplifier and a y-axis that represents increasing outputpower from the power amplifier. The power amplifier employed is of atype used in RF communications and the like, such as the power amplifier120, described above.

Line 602 represents behavior of the power amplifier (withoutlinearization). It can be seen that the behavior is again non-linear.This is an example of typical power amplifier exhibiting non-linearbehavior without correction. Line 604 represents behavior from anon-linear pre-distorter. The pre-distortion 604 compensates fordistortions introduced by the power amplifier.

The combination of the pre-distortion and the power amplifier behavioris represented by line 606. The combination 606 is the result of thepower amplifier characteristics and the non-linear pre-distortionengine. It can be seen that the combination 606 is substantially linear.

The combination 606 yields a constant peak power P _(out) at theamplifier output. Peak input power is denoted as {circumflex over(P)}_(in) and average input power is denoted as P _(in). The peak toaverage power ratio during the initial phase, where t<T, is

${PAPR}_{i\; n} = {\frac{{\hat{P}}_{i\; n}}{{\overset{\_}{P}}_{i\; n}}.}$

During the initial phase, as described above, no pre-distortion orlinearization is applied. Automatic peak scaling by the CFRP makes surethe peak power before linearization, denoted {circumflex over (P)}_(in),is equal to the peak power after linearization denoted {circumflex over(P)}_(in)′. After the initial phase, the combination or chain 606, whichincludes a combination of 602 and 604, is substantially linear yieldingthe same peak power {circumflex over (P)}_(out) a the power amplifieroutput. The peak power is kept constant, so the average power drops byΔP from P _(out) to P _(out)−ΔP.

The graph 600 is depicted with a vertical line at the average poweramplifier input P _(in). Under the constant average power approach, thecompensation 606 would lie through an intersection of the average poweramplifier input P _(in) and the average power amplifier output P _(out).However, using the constant peak power approach, the compensation 606 isshifted by the power drop ΔP as shown. As a result, linearity of thechain consisting of pre-distorter and power amplifier in this approachis maintained throughout the range while keeping control of the peakpower at the power amplifier input (or equivalently, the pre-distorteroutput) and thus avoiding undesired avalanche or pre-distorter blow-upeffects. FIG. 7 is a flow diagram illustrating a method 700 of operatinga non-linear pre-distortion engine having constant peak power. Themethod applies a pre-distortion such that a substantially constant peakpower is used.

The method 700 begins at block 702 where a time aligned signal isgenerated from an RF output signal from a power amplifier. A coupledversion of the RF output signal is typically used. The RF output signalis generated by the power amplifier, which has non-linearcharacteristics. A time alignment component aligns the time alignedsignal with another signal, such as an input signal.

A peak normalized signal is generated by a peak normalizer at block 704.The peak normalizer identifies a max or peak value or estimate for anumber of samples of the time aligned signal. Then, the samples aredivided by a max value of the number of samples to obtain the peaknormalized signal. Typically, the peak normalized signal has values lessthan or equal to one.

A peak estimator generates a peak estimate of the input signal at block706. The input signal is a signal with modulation components, such asamplitude modulation components, that convey information. The peakestimate is a max or peak value of a number of values. Typically, thenumber of values comprise a block. The size of the block can vary.

A feedback signal is generated at block 708 as a combination of the peaknormalized signal and the peak estimate. It is noted that the peaknormalized signal is based on the RF output signal and the peak estimateis based on the input signal. A summation component is used to combinethe signals into the feedback signal.

A compression estimator generates a compression estimate at block 710.The compression estimate is based on the input signal and the feedbacksignal. In one example, the compression estimate is a ratio of anaverage power of the input signal divided by an average power of thefeedback signal. Examples of suitable compression estimators aredescribed above.

A crest factor of the input signal is reduced by a crest factorreduction processor at block 712 based on the compression estimate. Thecrest factor reduction processor generates a reduced crest factor signalas an output. The reduced crest factor signal has a reduced crest factoraccording to the compression estimate and/or other requirements, such asEVM and the like.

A digital pre-distorter generates a pre-distorted signal from the crestfactor reduced signal according to pre-distortion parameters to generatea pre-distorted signal at block 714. An example of the pre-distortedsignal is given by line 604 of FIG. 6. The pre-distorted signal ismodified or distorted to compensate for nonlinearity of the poweramplifier.

The power amplifier then generates the RF output signal from thepre-distorted signal. Due to the pre-distortion, the RF output signal isgenerated with a substantially linear relationship by the chain to theinput signal.

Additionally, a second digital pre-distorter generates a secondpre-distorted signal based on the peak normalized signal. A learningalgorithm component generates the pre-distortion parameters based on thepre-distorted signal and the second pre-distorted signal. Thepre-distorted signal and the second pre-distorted signal should besubstantially similar. Differences therein are noted by the learningalgorithm component, which alters or adjusts the pre-distortionparameters to compensate.

While the method is illustrated and described below as a series of actsor events, it will be appreciated that the illustrated ordering of suchacts or events are not to be interpreted in a limiting sense. Forexample, some acts may occur in different orders and/or concurrentlywith other acts or events apart from those illustrated and/or describedherein. In addition, not all illustrated acts may be required toimplement one or more aspects or embodiments of the disclosure herein.Also, one or more of the acts depicted herein may be carried out in oneor more separate acts and/or phases.

It is appreciated that the claimed subject matter may be implemented asa method, apparatus, or article of manufacture using standardprogramming and/or engineering techniques to produce software, firmware,hardware, or any combination thereof to control a computer to implementthe disclosed subject matter (e.g., the systems, arrangements and thelike shown in FIGS. 1, 2, etc., are non-limiting examples that may beused to implement the above methods). The term “article of manufacture”as used herein is intended to encompass a computer program accessiblefrom any computer-readable device, carrier, or media. Of course, thoseskilled in the art will recognize many modifications may be made to thisconfiguration without departing from the scope or spirit of the claimedsubject matter.

A non-linear pre-distortion engine having constant peak power isdisclosed. The engine includes a compression estimator, a crest factorreduction processor, a digital pre-distorter and a power amplifier. Thecompression estimator is configured to generate a compression estimatebased on an input signal and a feedback signal. The feedback signal isbased on an RF output signal. The crest factor reduction processor isconfigured to reduce a crest factor of the input signal to generate acrest factor reduced signal based on the compression estimate. Thedigital pre-distorter is configured to apply a pre-distortion to thecrest factor reduced signal after an initial phase and generate apre-distorted signal based on pre-distortion parameters. The poweramplifier is configured to amplify the pre-distorted signal to generatethe RF output signal. The operation of the chain consisting ofpre-distorter and power amplifier is substantially linear and operatesbased on a constant peak power.

A compression estimator includes a first input, a first absolute valuecomponent, a first summation component and a first integrator. The firstinput is configured to receive a first signal. The first absolute valuecomponent is configured to generate a first absolute value of the firstsignal. The first summation component is configured to add the firstabsolute value to a first integrator output signal to generate a firstsummation signal. The first integrator is configured to integrate thefirst summation signal and generate the first integrator output signal.The first integrator output signal is an average power of the firstinput signal.

A method of operating a non-linear pre-distortion engine having constantpeak power is disclosed. A time aligned signal is generated from an RFoutput signal. A peak normalized signal is generated by a peaknormalizer. A peak estimate of an input signal is generated by a peakestimator. A feedback signal is generated as a combination of the peaknormalized signal and the peak estimate. A compression estimate isgenerated as a ratio of an average power of the input signal and anaverage power of the feedback signal. A crest factor of the input signalis reduced to generate a crest factor reduced signal by a crest factorreduction processor according to the compression estimate.

In particular regard to the various functions performed by the abovedescribed components or structures (assemblies, devices, circuits,systems, etc.), the terms (including a reference to a “means”) used todescribe such components are intended to correspond, unless otherwiseindicated, to any component or structure which performs the specifiedfunction of the described component (e.g., that is functionallyequivalent), even though not structurally equivalent to the disclosedstructure which performs the function in the herein illustratedexemplary implementations of the invention. In addition, while aparticular feature of the invention may have been disclosed with respectto only one of several implementations, such feature may be combinedwith one or more other features of the other implementations as may bedesired and advantageous for any given or particular application.Furthermore, to the extent that the terms “including”, “includes”,“having”, “has”, “with”, or variants thereof are used in either thedetailed description and the claims, such terms are intended to beinclusive in a manner similar to the term “comprising”.

1. A non-linear pre-distortion engine maintaining constant peak power atits output, the engine comprising: a compression estimator configured togenerate a compression estimate based on an input signal and a feedbacksignal, wherein the feedback signal is based on an RF output signal; acrest factor reduction processor configured to reduce a crest factor ofthe input signal to generate a crest factor reduced signal based on thecompression estimate; a digital pre-distorter configured to apply apre-distortion to the crest factor reduced signal after an initial phaseand generate a pre-distorted signal based on pre-distortion parameters;a power amplifier configured to amplify the pre-distorted signal togenerate the RF output signal, wherein the operation of the poweramplifier is substantially linear and operates based on a constant peakpower; and a multiplier and a peak estimator, wherein the peak estimatoris configured to generate a peak estimate of the input signal and themultiplier is configured to generate the feedback signal at leastpartially based on the peak estimate.
 2. (canceled)
 3. The engine ofclaim 1, wherein the peak estimate is configured to generate the peakestimate using interpolation to identify a peak value over a block ofsamples.
 4. A non-linear pre-distortion engine maintaining constant peakpower at its output, the engine comprising: a compression estimatorconfigured to generate a compression estimate based on an input signaland a feedback signal, wherein the feedback signal is based on an RFoutput signal; a crest factor reduction processor configured to reduce acrest factor of the input signal to generate a crest factor reducedsignal based on the compression estimate; a digital pre-distorterconfigured to apply a pre-distortion to the crest factor reduced signalafter an initial phase and generate a pre-distorted signal based onpre-distortion parameters; a power amplifier configured to amplify thepre-distorted signal to generate the RF output signal, wherein theoperation of the power amplifier is substantially linear and operatesbased on a constant peak power; and a peak normalizer configured togenerate a peak normalized signal based on the RF output signal.
 5. Theengine of claim 4, further comprising a multiplier configured togenerate the feedback signal based on the peak normalized signal and apeak estimate.
 6. The engine of claim 4, further comprising a multiplierconfigured to generate a feedback pre-distortion signal based on thepeak normalized signal and a peak estimate of the pre-distorted signalprovided to the power amplifier.
 7. The engine of claim 6, furthercomprising a learning algorithm component and a second digitalpre-distorter, wherein the second digital pre-distorter generates asecond pre-distorted signal based on the pre-distortion parameters andthe peak normalized signal and the learning algorithm component isconfigured to generate the pre-distortion parameters based on acombination of the pre-distorted signal and the second pre-distortedsignal.
 8. A non-linear pre-distortion engine maintaining constant peakpower at its output, the engine comprising: a compression estimatorconfigured to generate a compression estimate based on an input signaland a feedback signal, wherein the feedback signal is based on an RFoutput signal; a crest factor reduction processor configured to reduce acrest factor of the input signal to generate a crest factor reducedsignal based on the compression estimate; a digital pre-distorterconfigured to apply a pre-distortion to the crest factor reduced signalafter an initial phase and generate a pre-distorted signal based onpre-distortion parameters; a power amplifier configured to amplify thepre-distorted signal to generate the RF output signal, wherein theoperation of the power amplifier is substantially linear and operatesbased on a constant peak power; and a time align component configured totime align a coupled version of the RF output signal into a time alignedsignal and the feedback signal is at least partially based on the timealigned signal.
 9. The engine of claim 1, wherein the crest factorreduction processor is also configured to adjust the crest factor tofulfill requirements.
 10. The engine of claim 9, wherein therequirements include error vector magnitude requirements.
 11. The engineof claim 1, wherein the compression estimate is a ratio of an averagepower of the input signal and an average power of the feedback signal.12-20. (canceled)
 21. The engine of claim 1, further comprising a peaknormalizer configured to normalize a time aligned RF output signal withrespect to its peaks to generate a peak normalized signal from the RFoutput signal.
 22. The engine of claim 21, where the multiplier isconfigured to combine the peak normalized signal with the peak estimateto generate the feedback signal.